Embodiments of the present invention relate to a non-volatile memory device configured to use the Low Power Double Data Rate (LPDDR) 2 specification.
Memory devices can be classified into a volatile memory device and a non-volatile memory device. The non-volatile memory device uses a non-volatile memory cell capable of preserving stored data without a power supply. For example, the non-volatile memory device may be implemented as a flash Random Access Memory (Flash RAM), a Phase Change Random Access Memory (PCRAM), or the like.
The PCRAM is a memory cell which uses a phase change material such as germanium antimony tellurium (GST) whose phase is inter-changeable between a crystalline phase and an amorphous phase depending on the temperature applied to the GST.
A non-volatile memory, e.g., a magnetic memory, a phase change memory (PCM), or the like, has a data processing speed similar to that of a volatile RAM. The non-volatile memory also preserves data even when power is turned off.
FIGS. 1A and 1B illustrate a conventional Phase Change Resistor (PCR).
Referring to FIGS. 1A and 1B, the phase change resistor (PCR) 4 includes a top electrode 1, a bottom electrode 3, and a phase change material (PCM) layer 2 located between the top electrode 1 and the bottom electrode 3. If a voltage and current are applied to the top electrode 1 and the bottom electrode 3, a current signal and a high temperature are provided to the PCM layer 2 such that an electrical conductive status of the PCM layer 2 is changed.
FIGS. 2A and 2B illustrate data storage operation of a conventional phase change resistor (PCR).
Referring to FIG. 2A, when a low current below a threshold value is applied to the phase change resistor (PCR) 4, the PCM layer 2 is kept at a temperature suitable for a crystalline phase. Therefore, the PCM layer 2 is in a crystalline phase with low-resistance. As a result, a current may flow between the top electrode 1 and the bottom electrode 3.
On the other hand, as shown in FIG. 2B, when a high current higher than the threshold value is applied to the phase change resistor (PCR) 4, the PCM layer 2 is at a temperature higher than a melting point. Therefore, the PCM layer 2 is in an amorphous phase with high-resistance. As a result, it is difficult for the current to flow between the top electrode 1 and the bottom electrode 3.
Therefore, the PCR 4 may store data corresponding to two resistance phases. For example, when the PCR 4 in a low-resistance phase is set to data ‘1’ and the PCR 4 in a high-resistance phase is set to data ‘0’, the PCR 4 may store two logic states for data.
In addition, a phase of the PCM layer (i.e., a phase change resistive material) 2 is not changed although power to the phase change memory is cut off, and thus data can be stored in a non-volatile manner.
FIG. 3 illustrates a write operation of the conventional Phase Change Resistor (PCR) cell.
Referring to FIG. 3, when a current flows between the top electrode 1 and the bottom electrode 3 of the PCR 4 during a predetermined time, heat is generated.
Assuming that a low current below a threshold value flows in the PCR 4 during a predetermined time, the phase change material 2 is at a crystalline phase due to a low-temperature applied, and thus the PCR 4 serving as a low-resistance element is at a set status.
Otherwise, assuming that a high current higher than the threshold value flows in the PCR 4 during the predetermined time, the phase change material (i.e., PCM layer) 2 is at an amorphous phase due to a high-temperature, and thus the PCR 4 is at a reset status.
By means of the aforementioned properties, in order for data of the set status to be written during a write operation mode, a low voltage is applied to the PCR 4 for a long period of time. On the other hand, in order for data of the reset status to be written during the write operation mode, a high voltage is applied to the PCR 4 for a short period of time.
The phase change resistance (PCR) memory outputs a sensing current to the PCR 4 during the sensing operation, such that it can sense data written in the PCR 4.